1. Field of the invention
The present invention is related to a method of increasing image gray-scale response speed, and especially to a method which divides a scanning area of an LCD into a plurality of areas, respectively applies an advance voltage to overdrive, or a data voltage to maintain the brightness of the data during a time period of synchronized signals, thereby to achieve an object of speeding up driving of the LCD and to increase the gray-scale response speed. The method suits for treatment of frames of displays of various LCD's and displays of organic light emitting diodes (OLED's).
2. Description of the Prior Art
In the earlier stage, people mostly are satisfied with that LCD's are light and without radiation. Following advancing of techniques and after appearing of LCD's of large sizes, LCD's are widely used in life and audio and video amusements, people gradually pay attentions to the requirements of the parameters such as of wide visual angle and response times. By the fact that it uses liquid crystal molecules as their basic elements in LCD's, such molecules of an intermediate state between the solid and the liquid states not only have the feature of being subjected to flowing by the action of an external force, but also have the feature of optical anisotropy specific for crystals, thereby they can make the arrangement of the crystals change to other directions by adding electric fields, and thereby result change of optical features during penetration of the light beams through the LCD's. Such a phenomenon of generating optical modulation by using added electric fields is called the photoelectric effect of LCD's.
Referring to FIGS. 1A and 1B showing a simple schematic view of the structure of an LCD, wherein the LCD panel 10 is provided thereon with source drivers 11 for converting adjusted gray-scale signal data into corresponding data voltages, and for outputting image signals through a plurality of data lines 111 of the source drivers 11 to the LCD panel 10. The LCD panel 10 is provided at a side thereof with gate drivers 12 for continuously supplying scanning signals, and for transmitting the scanning signals to the LCD panel 10 through a plurality of gate lines 121 connecting with the gate drivers 12; the data lines 111 cross perpendicularly to the gate lines 121. The area surrounded is a pixel matrix 13.
When the image signals are sent out of the source drivers 11, they provide a source electrode for a transistor Q1 in the pixel matrix 13 through a data line D1; and the gate drivers 12 also send out control signals relatively for a gate electrode of the transistor Q1 through a gate line G1. Then output an output voltage value through a circuit in the pixel matrix 13. A reaction of the liquid crystal molecules in correspondence with the pixel matrix 13 is activated, the liquid crystal molecules located between two glass base plates of the LCD panel 10 forms a parallel-plate capacitor of a liquid crystal CLC. By virtue that the capacitor CLC is unable to keep voltage for the next time when it is to update frame data, hence a storage capacitor CS is added to render the capacitor CLC to keep the voltage for the next time when it is to update the frame data.
Superiority or inferiority of the performance of the LCD has an index-response time. Generally it has two conditions when there is no voltage applied to the LCD: a normally white (NW) mode and a normally black (NB) mode. The normally white (NW) mode means that a frame is pervious to light when the LCD panel 10 is not applied with a voltage, in which the frame is a bright frame. The normally black (NB) mode means that a frame is obscured when the LCD panel 10 is not applied with a voltage, in which the frame is an all-black frame. Taking the normally white (NW) mode as an example, the response time can be divided into two kinds:
(1) ascending response time: the twisting time required for the liquid crystal when the brightness of a liquid crystal box of the LCD is changed from 90% to 10% under application of a voltage, this is called in abbreviation as “Tr”; and
(2) descending response time: the time required for the liquid crystal when the brightness of the liquid crystal box of the LCD is restored from 10% to 90% under application of no voltage, this is called in abbreviation as “Tf”.
Generally, when the speed of displaying of the frames is over 25 frames/sec, human eyes will take the fast changing frames as continuous sequential pictures. In modern family amusements, for example, in playing DVD pictures of high quality or in playing games with fast moving frames, the speed of displaying of the frames is above 60 frames/sec. In other words, the frame interval time is 1/60=16.67 ms, if the response time of an LCD is larger than the frame interval time, there will be traces of residual images or skipping to seriously affect the quality of viewing images. As to how to increase the speed of response, it shall be counted on the factor that affects the response time. The followings are respectively the calculation formulas for the ascending response time Tr and the descending response time Tf:
      Tr    =                            r          1                ⁢                  d          2                            Δɛ        ⁡                  (                                    V              2                        -                          V              th              2                                )                      ,          ⁢            T      f        =                            r          1                ⁢                  d          2                            Δɛ        ⁢                                  ⁢                  V          th          2                    
in which r1 is a coefficient of viscosity of the crystal material; d is a gap of the liquid crystal box; V is a driving voltage of the liquid crystal box; and Δε is a dielectric coefficient of the liquid crystal material.
We can see from the above equations that there are four ways to reduce the response time of the LCD: namely, lowering the coefficient of viscosity, reducing the gap of the liquid crystal box, increasing the driving voltage and increasing the dielectric coefficient. Wherein the technique of increasing the driving voltage is called as the technique of “overdrive” with which an integrated circuit driven by the liquid crystal (driver IC) transmits an increased voltage to a liquid crystal panel to increase the twisting voltage of the liquid crystal. Thereby the liquid crystal can be faster twisted and recovered to quickly get the desired brightness to be presented of the image data.
Referring to FIG. 2 showing variation curves of brightness versus time under different driving voltages, wherein L1 is the desired brightness to be presented of the image data, the curve of data voltage V2 presenting the desired brightness by driving the liquid crystal molecules is marked with 22, the time for getting this brightness is t0. In order to reduce the time for getting this brightness, the variation of gray-scale brightness of the LCD measured in advance is referenced to provide a driving voltages V4 with its strength increased, the curve is shown by the FIG. 24. Thereby the time t0 for getting this desired brightness is reduced to t1, and this is the method of “overdrive” technique.
The inventor of the present invention provided a brand new method of increasing image gray-scale response speed based on his professional experience of years in studying and developing in this art and using such a concept of “overdrive”, in order to get a whole better effect of increasing the image gray-scale response speed.